what is the purpose of the O2 sensor?....if I hook up my A/F gauge to the sensor and to the connector on the wire harness I get no reading on the A/F gauge except a slight dim red bar all the way on lean. but if I disconnect the plug to the computer the A/F gauge works fine and seems to give me good readings ....slight rich on excel..... stoich. on maintaining speed....and lean when slowing.
how does the computer know the right mixture if the O2 sensor isn't even connected to it?
also should it read lean or off the gauge under idle? prob. not, my idle ranges up and down from 750 to 900 in that area in is barely showing on the gauge. But as soon as I give it a little gas and get it over 1K its Stoich.

Oh yeah.....87 N/A with a 90 motor in it.

thanks for any help

 

When cruising at light load (not idle or accelerating) the ECU goes into closed-loop mode and uses the O2 sensor to try to maintain stiochiometric mixtures. You can see it on the meter as a rapid fluctuation between slightly rich and slightly lean. It's for economy only. Sounds like you might have wired it funny. What did you do exactly?